The U.S. jobless rate dropped sharply in December to 6.7 percent, its lowest point in more than five years, but employers added just 74,000 new workers to their payrolls.
The government said Friday that unemployment dropped from 7 percent in November.
However, the U.S. labor statistics chief, Erica Groshen, said two-thirds of the decline in the jobless rate was accounted for by workers ending their search for new jobs, and thus not being counted by the government in the jobless number.
She told a congressional economic panel the reason for the dip in the jobless rate is a troubling sign for the U.S. economy.
"It's not as robust a sign as if the fall in unemployment had come from creation of a lot of jobs.... It's certainly not a sign of strength."
The country's unemployment rate has been above 7 percent since the first signs of the country's steep recession in late 2008, but declined 1.2 percentage points over the course of 2013.
Economists had predicted that the labor market would add 191,000 jobs last month after robust hiring in October and November. But the scant number of new workers signaled that the U.S. economy slowed in the final weeks of 2013.
The U.S. economy has been steadily, if somewhat unevenly, advancing over the last several months.
Janet Yellen, who takes over next month as chair of the Federal Reserve, the country's central bank, says policy makers are hopeful that the American economy will advance by 3 percent or more this year. That would be up from the 2.6 percent figure recorded through the first nine months of 2013.
For more than a year, the Fed purchased securities worth $85 billion a month to pump more money into the economy in an attempt to boost job growth and keep interest rates low. But now, as the recovery from the country's recession gains some strength, the central bank has started to trim its direct support of the economy. It cut purchase of the securities this month to $75 billion, and policy makers have planned to end the program over the course of 2014 if the economy keeps advancing.
However, December's weak job growth could lead the Fed to rethink its strategy.
Even as the economy has improved, 10.4 million workers remain unemployed, many of them for lengthy periods of time. U.S. President Barack Obama and Republican lawmakers in Congress remain locked in a dispute over whether to extend unemployment compensation to the long-term unemployed.
About 1.3 million workers lost their benefits in late December, and more would in the coming months if the program is not extended.